Update: I was unfortunately not aware of Shamus Young's severe criticism of Fallout 3 available here to link in the original piece and I regret that. It dovetails rather nicely with what I've written and it's much better executed than my piece. I strongly recommend anyone...

Remember the sheer badassery of John Marston? Remember that moment when you were just like John is the most manly cowboy since...ever? Seriously, nothing you do could make him not a badass. Even...let's say for argument sake...putting him in his underwear. He'd still be the coolest cowboy ever. Cooler than Cowboy Curtis. He'd just be a cool cowboy kickin' it in his long johns. But what else could make it just that little bit better/more ridiculous and yet still badass?

He's your only friend in the Forbidden Lands. It feels reassuring to have him with you during the colossi fight. I remembered trying to take out the Desert Dragon and looking down to see Argo racing along side it trying to catch up. What an animal.

Worst:
Dogmeat (the original Fallouts)

He's not that bad in Fallout 3 especially if you install a dog pack mod. However, in the original Fallouts unless you save scumm, he's going to die, it's going to be bloody, and it's going to be heartbreaking.

You step into town, fresh from your journey and eager to start your new life in a town of animals when up waltzes the crimelord, persuading you to buy a rundown shack of a hovel and instead of it as a gift, there's a ginormous price tag for the one storey 8x8 cardboard box you now call a home. He says "Don't worry, pay it off whenever" but what he really means is "Pay it off quick or I'll break your knees". The guy owns the town! He wouldn't even upgrade his store to get the good shit until you buy enough from him! And once you do pay off your blood debt, he upgrades your home while you're sleeping and creates a new debt for it! The cycle only ends when you pay off your debt for a three-tier crib with multiple rooms and getting an out-of-towner to buy some Nook goods for the last level of his crime franchise.

And in Wild World, he conscripts his nephews as his coon goons, you just know they wack people at night.

Everything that my kindred spirit cyberjim said is exactly what I think. I never have felt as strong of an emotional connection to any game companion, animal or not, as I did with Agro. That horse was there for you, man. Dogmeat in Fallout 1 is the worst, not because he's a bad doggie, but because he's a stupid one who, before you can react, will run right up into a group of bad guys, bite one of them a few times for 1-3 damage each, and then get lit up by a burst of machine gun fire. Whether it's by your enemies or your own party, that dog is going to be violently killed._________________

But you can't think of the Animal Crossing townsfolk as animals, oddly, or else it gets too weird. They're really more like people. In fact, all the anthropomorphized animals mentioned so far shouldn't be included.

What about the dog you get in Fallout: New Vegas. I think his name is Rex, but not sure. Anyways leader of those Elvis impersonators gives him to you. I like that dog, because he's part cyborg._________________

Does Shadowmere count?
Because Shadowmere will fuck your shit up all day and all night long, and finish the main quest without you if necessary. Wouldn't even be a challenge._________________https://www.youtube.com/watch?v=tuluUJK9tHY
Oi

Shadowmere is a boss. I never did the Dark Brotherhood quest, but it was the first thing by brother did so he had Shadowmere with him for the entire game. He would jump off a cliff or stomp an old witch to death without a moment's hesitation.